1. Field of the Invention
The present invention relates to alternative fuels for internal combustion engines, and more specifically to blends of hydrogen in natural gas that are specially formulated to achieve specific advantages over pure natural gas or more tradition gasoline or diesel fuels.
2. Description of the Prior Art
The current predominant forms of fuel for internal combustion engines are derivatives of petroleum, namely gasoline and diesel fuel. However, the advancing depletion and unreliability of crude oil resources and significant environmental concerns resulting from the use of these fuels underscore the need for petroleum-independent alternative fuels. Primary U.S. alternative energy resources are reserves of natural gas and coal. Natural gas can be used directly as an alternative fuel for internal combustion engines, or it can be converted into other fuels, including hydrogen gas and liquid fuels, such as methanol (methyl alcohol). Coal is difficult to use directly as a fuel in internal combustion engines, although it can be converted to "coal gas" comprising primarily hydrogen and carbon monoxide or into liquid fuels, including methanol and synthetic petroleum.
Hydrogen, theoretically if not yet practically, is an attractive alternative for meeting future transportation energy requirements with renewable energy sources. Like electricity, hydrogen is an energy carrier, not a source of energy. Traditionally, hydrogen has been manufactured from natural gas or coal, although it is also produced by an electrical water-splitting process known as electrolysis that can be powered by any form of energy. Producing hydrogen as a transportation fuel from nonrenewable energy forms would improve urban air quality, but it would not solve resource problems. However, if hydrogen is derived from renewable energy sources, such as solar energy, wind energy, geothermal energy or ocean thermal energy, it can provide the basis for a perfectly balanced energy cycle:
(1) Electrolysis separates water, H.sub.2 O, into hydrogen and oxygen gases, H.sub.2 and O.sub.2 respectively according to the reaction 2H.sub.2 O.fwdarw.2H.sub.2 +O.sub.2. The oxygen may be vented or sold as a byproduct.
(2) Hydrogen is stored, transported, delivered to motor vehicles and burned to produce energy for powering the vehicles and water vapor as a by-product according to the net reaction 2H.sub.2 +O.sub.2 .fwdarw.2H.sub.2 O.
(3) The water vapor is released to the atmosphere where it eventually falls as precipitation, once again becoming available for electrolysis.
Hydrogen combustion produces no objectionable emissions other than trace amounts of nitrogen oxides that form when residual nitrogen and oxygen in air are heated in the combustion process. Even though prototype hydrogen vehicles have already passed the most strict standards for nitrogen oxide emissions, future hydrogen powered fuel cells may eventually propel motor vehicles with absolutely no nitrogen oxides at all.
Unfortunately, as wonderful as the hydrogen energy cycle may seem in theory, there are several practical drawbacks to the use of hydrogen that have impeded the implementation of hydrogen as a transportation fuel on any significant scale in the past and will continue to do so in the immediate future. Such drawbacks include the greater cost of hydrogen relative to conventional fuels, the difficulty and expense of storing hydrogen, which results in limited driving range, reduced power and operational problems when burned in engines designed for gasoline or diesel fuel, and the lack of a fuel distribution infrastructure. There is also an undeserved perception, sometimes dubbed the Hindenburg Syndrome, that hydrogen is significantly more dangerous than conventional fuels.
To overcome these difficulties and yet take advantage of the burning characteristics of hydrogen, there have been many studies and developments directed to the use of hydrogen in conjunction with conventional liquid petroleum fuels in internal combustion engines. Examples of these developments are disclosed or suggested by U.S. Pat. No. 1,112,188, issued to Atwood on Sept. 29, 1914; U.S. Pat. No. 1,379,077, issued to Blumenberg on May 24, 1921; U.S. Pat. No. 3,906,913 issued to Rupe on Sept. 23, 1975; U.S. Pat. No. 4,017,268, issued to Gilley on Apr. 12, 1977 and U.S. Pat. No. 4,573,435, issued to Shelton on Mar. 4, 1986. In the earlier of these patents, hydrogen was selected because of its effect as a combustion stimulant. In the more recent patents, hydrogen was selected because it is a cleaner burning fuel itself and because it reduces polluting emissions exhausted from gasoline engines.
Eccleston and Fleming reported on hydrogen/natural gas engine tests conducted under the U.S. Bureau of Mines Automotive Exhaust Emissions Program, Technical Progress Report 48, February, 1972. They were really proposing the use of hydrogen-rich synthetic coal gas as an automotive fuel, but they had no such fuel, so, for study purposes only, they simulated the coal gas by preparing mixtures of hydrogen in natural gas. They found that hydrogen reduced hydrocarbon, carbon monoxide, and nitrogen oxide emissions over a wide range of fuel/air mixtures, relative to pure natural gas.
However, the use of hydrogen in conjunction with conventional fuels have also been fraught with difficulties. For example, hydrogen is virtually insoluble in liquid hydrocarbons, such as gasoline or diesel fuel. It also cannot be dissolved in liquefied butane or liquefied propane to any significant extent, although it readily mixes with natural gas in compressed gas tanks. To avoid the necessity of having two fuel storage systems (one for hydrogen, one for the liquid fuel) numerous efforts have sought to break down liquid fuels in on-board reformers to make hydrogen-rich gaseous products. However, even though such processes are routinely carried out in the chemical process industry, they are extremely difficult to implement compactly aboard an automobile in a way that meets the rapid changes in an automobile's fuel demand. Therefore, contemporary alternative fuels programs before this invention have been proceeding without the benefit of clean burning renewable hydrogen.
Because of the fledgling nature of distribution systems for alternative fuels, such as methanol or natural gas, for burning in automobiles, it is advantageous for alternative fuel vehicles to operate on conventional fuels as well. However, the alternative fuels known and used prior to this invention have substantially different burn or combustion rates than the conventional fuels. For example, natural gas, which is considered to be one of the major alternative fuels for at least the near future, and conventional gasoline burn at significantly different rates in internal combustion engines thus requiring substantial engine modifications and adjustments to burn one fuel or the other. At a fixed rotating speed (RPM), manifold vacuum and "equivalence ratio" (the fuel/air ratio as a fraction of the chemically correct or stoichiometric ratio), natural gas burns more slowly than gasoline in a given engine. A number of factors influence the rate of combustion in the cylinder of an engine, but optimum ignition timing should be set where it ignites the fuel soon enough so that the peak combustion pressure occurs about 10.degree. to 15.degree. of crank rotation after the piston passes top-dead-center on the combustion stroke. Because natural gas burns more slowly than conventional gasoline, vehicles with dual fuel engine systems for burning either natural gas or gasoline must have at least some means for advancing the ignition timing to meet the requirements of natural gas and for retarding the timing for optimum gasoline combustion. This requirement presents several technical difficulties, including the need for sophisticated engine control systems that adjust the fuel/air mixture and ignition timing according to the requirements of both the alternative and conventional fuels. Some existing state of the art computerized gasoline engine control systems, when operating in the "closed loop" mode, automatically advance the ignition timing in search of the most efficient operating conditions. If the automatic controls have enough range, they might meet the spark advance requirements of natural gas operation, at least some of the time. At other times, in the "open loop" mode, the ignition timing may be set by the microprocessor to predetermined values that are approximately correct for gasoline under a given set of operating conditions. At such times the spark delivery will be too late for efficient, low emissions operation on natural gas.
There is an aftermarket device called Dual Curve Ignitions offered by Autotronic Controls Corporation, El Paso, Tex., that changes the ignition timing of the engine when it is switched from gasoline to natural gas and back again. However, since there are so many different types of ignition systems in the myriad of different automobiles that may be converted to natural gas in the future, it is impossible for a single device to serve all of them with optimum ignition timing for both gasoline and natural gas. Ford Motor Company is also developing an advanced control system for its "Flexible Fuel Vehicle" that measures the ratio of methanol/gasoline flowing to the engine, computes the correct fuel/air mixture and ignition timing (vastly different for the two fuels), and instructs the engine's electronic controls to make the necessary adjustments. Such sophistication is cost-effective only on a mass-produced basis. Even then, there are so many other engine design features built into the permanent structures of engines by manufacturers based on optimum performance criteria at a conventional fuel burn rate and which cannot be changed, that simple adjustment of fuel-air ratios and spark timing still do not result in efficient running engines when the alternate fuel is burned.
Alternative fuels for diesel or compression ignition engines are also of interest for reducing urban air pollution and dependence on petroleum. In addition to modified petroleum oils, vegetable oils and other liquids are being evaluated for their potential to reduce diesel exhaust emissions. Natural gas is also used in diesel engines by a process known as fumigation wherein gaseous fuel is metered into the intake air stream. However, natural gas does not ignite efficiently by compression. Therefore, when operating on natural gas, a small amount of diesel fuel still is injected into the combustion chamber to ignite the natural gas/air mixture, i.e., acting in lieu of spark plugs. Burning other fuels, such as methanol or natural gas in conjunction with diesel fuel, has been shown to decrease particulate emissions (smoke) and nitrogen oxides, but it also increases harmful carbon monoxide and organic gases.
Hydrogen has also been tried as a supplement to diesel fuel. For example, in the 1920's and 1930l3 s engines of hydrogen filled dirigible air ships burned some hydrogen with diesel fuel. In flight, the loss in weight due to diesel fuel consumption had to be countered by releasing hydrogen to maintain neutral buoyancy. Rather than simply venting the hydrogen to the atmosphere, it was fumigated into the engines, which had the effect of extending the range of the airships. Laboratory studies of hydrogen in diesels have continued to the present, but prior to this invention there have been no real positive or promising hydrogen fumigant or natural gas fumigant techniques for diesel engines that would be both economical as well as provide significantly improved exhaust emission.